This invention relates generally to systems and methods for managing direct current (xe2x80x9cDCxe2x80x9d) power. More specifically, this invention relates to DC to DC converters and power management systems and methods.
Today, most hybrid fuel cell/battery power systems, and other systems having multiple DC power sources and batteries, are arranged as shown in FIG. 1. The arrangement shown in FIG. 1 is referred to as the xe2x80x9cbattery nodexe2x80x9d approach because the power must pass through the battery output node at the battery voltage. This configuration therefore uses battery charge controller and inverter ratings that match the capacity of the fuel cell.
Conventional DC to DC converters and their associated inverter designs and products have several deficiencies that make it difficult for them to adequately meet the functional requirements of modern hybrid power systems. These conventional converters are therefore unable to satisfy the needs of a typical energy user. Among other problems, conventional DC to DC converters typically generate electrical noise and high frequency ripple currents on the input (source) and output (load) busses. They are also poorly adapted to the regulation of input current. Furthermore, they typically exhibit energy conversion efficiencies of only around 80-90%.
According to one aspect of this invention, a DC to DC Buck and Boost Converter is provided. xe2x80x9cBuckxe2x80x9d power conversion refers to a reduction in voltage from an input side of the converter to an output side. xe2x80x9cBoostxe2x80x9d power conversion refers to an increase in voltage from the input side to the output side of the converter. According to one embodiment of this invention, the Buck and Boost DC to DC Converter includes an electrical circuit that allows batteries and other electrical energy storage devices to be charged from or to discharge to a variable voltage DC bus. This electrical circuit can also be configured to enable seamless integration with other energy storage devices and/or DC power sources, such as fuel cells, to provide DC power for a Power Management System.
Improved Boost DC to DC Converters are also provided which reduce noise and ripple currents in low voltage/high current applications. According to one embodiment, a resonant capacitance is provided by two resonant capacitors which store voltage using switches that permit zero voltage switching. According to another embodiment, an input capacitor is provided to maintain a constant voltage input to a resonant circuit. The addition of the input capacitor reduces voltage stress in a switching circuit.
A DC to DC Converter is provided in a module of a Power Management System. The Power Management System preferably provides both full power source management and power conditioning. In other words, the Power Management System preferably manages power flow to and from multiple, isolated DC power sources and energy storage devices, while delivering high quality alternating current (xe2x80x9cACxe2x80x9d) power to a load.